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Close encounters between stars and Massive Black Holes

Close encounters between stars and Massive Black Holes. Clovis Hopman Weizmann Institute of Science Israel. Advisor : Tal Alexander. Dissipative stellar processes near Massive Black Holes. Tidally powered stars in the Galactic Center Ultraluminous X-ray sources

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Close encounters between stars and Massive Black Holes

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  1. Close encounters between stars and Massive Black Holes Clovis Hopman Weizmann Institute of Science Israel Advisor: Tal Alexander

  2. Dissipative stellar processes near Massive Black Holes • Tidally powered stars in the Galactic Center • Ultraluminous X-ray sources • Gravitational Wave Radiation

  3. The stellar cusp near a BH

  4. Tides and Gravity Waves GWR Tides

  5. How to get near a Massive BH

  6. Race between inspiral and scattering Alexander & Hopman, ApJL 2003

  7. Kozai mechanism near MBHs Deviations from spherical symmetry in GC? Kozai eccentricity oscillations drive stars effectively towards the MBH (Hopman, Subr & Alexander 2005, in prep.)

  8. Squeezars: Tidal Power

  9. Surviving tidal heating Squeezars in Galactic Centers are transient sources Survival: low mass MBHs and efficient cooling

  10. Squeezars • Stars powered by tidal “squeezing” • Squeezars observable in Galactic Center (Alexander & Morris, ApJL 2003) • ~ 1 squeezar in GC (Alexander & Hopman, ApJL 2003) • Kozai: many more squeezars? (Hopman, Subr & Alexander 2005, in prep.) • Squeezars evaporate near MBHs

  11. Ultraluminous X-ray Sources Super Eddington luminosities IBH: engine of ULX? IBH can be formed dynamically in cluster (Portegies Zwart et al., Nature 2004)

  12. What feeds the IBH?? Clusters contain too little gas Tidal disruption of star gives only short (~yr) flare (Rees, Nature 1988) Solution: Tidal Capture!

  13. ULX: IBH fed by a tidally captured star Circularization possible around IBH Roche lobe overflow supplies gas ULX can switch on after cluster evaporates Lifetime and luminosity as observed

  14. Circularization Hopman, Portegies Zwart & Alexander, ApJL 2004 N-body simulations show tidal capture(Baumgardt, Hopman & Portegies Zwart 2005, in prep.)

  15. Rate independent of relaxation time Hopman, Portegies Zwart & Alexander, ApJL 2004 Captured Stars Probability = Capture Rate Stellar Lifetime 10 %

  16. Hopman, Portegies Zwart & Alexander, ApJL 2004 Mass Transfer and Luminosity

  17. Gravitational Wave Radiation

  18. Hopman & Alexander, astro-ph/0503672 . Monte Carlo tracks in phase space Stars perform random walk in phase space Length scale ac delimits volume of inspiral stars

  19. Eccentricity of LISA stars Barack & Cutler, PRD 2004

  20. Hopman & Alexander, astro-ph/0503672 . LISA Stars in the Strong Gravity Regime Massive Black Holes: Intermediate Mass Black Holes:

  21. Hopman & Alexander, astro-ph/0503672 . • Mass segregation: Heavy stars closer to MBH! • Rate independent of relaxation time • Orbits are very eccentric • Probably no signal from IBHs

  22. Conclusions Squeezars observable in Galactic Center Tidally captured stars around IBHs may be the engine that powers ULXs LISA stars will be highly eccentric

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